Return ReadableStream

[jimmywarting]

How about actually get a ReadableStream back instead of writing a own custom onChunk callback

With ReadableStream you would be able to pipeTo & pipeThrogh others streams
With web-stream-polyfill (npm) this would be a breeze

[jimmywarting]

with regards to #19 (cancellation) the way you would do it with ReadableStream is by calling .error() that would trigger xhr.abort

[jimmywarting]

Played a bit myself with streams and monkey patching xhr:

This is how i would do it for firefox: https://jsfiddle.net/98L105v3/2/

[jonnyreeves]

Thanks @jimmywarting this was an excellent suggestion; I've incorporated your ideas into #20 - I would appreciate your feedback and also any input you and @ariutta have on the future surface API of this library.

[jimmywarting]

Now when i look back at my monkey patch I like it since you can choose to overide it or get a new extended xhr (: